Replace Object#tee with more conventional Object#tap in specs

The spec_helper.rb defines an Object#tee method, which is functionally equivalent to Object#tap. Object#tap was added to Ruby 1.9 and to 1.8.7.

Attached is a patch that replaces the usage of 'tee' with 'tap' and will define the 'tap' method if it's missing (should only happen when Ruby 1.8.6 or below is used). If there's no need to support such a low minimum, this could be removed.